A circuit configuration for decoupling an electronic device from a data line in a motor vehicle is described, e.g., in published German patent document DE 198 33 462. The electronic device and at least one additional electrical system exchange data via the data line, during the operation of the electronic device. In the case of the circuit configuration where vehicle operation can be maintained despite a malfunction of an electronic device connected to the data line, the electronic device is connected to a fault detection device. In response to the fault detection device ascertaining a fault of the electronic device, the electronic device is decoupled from the data line by the circuit configuration, the serviceability of the electronic system being maintained.
In published German patent document DE 198 33 462 the important aspect is the monitoring of the data line and the detection of errors in the data line, which could impair the operability of the electronic device that is connected to the data line. The error detection device is switched into the data line for decoupling the electronic device from the data line in the error case, and it includes electrical switching elements so as to be able to cut off the data line in case of error. That assumes, however, that in each data line to which the electronic device is connected and which is supposed to be cut off in the error case, switching elements have to be situated.
Published German patent document DE 100 30 996 describes an arrangement in which the functional monitoring of the functional unit by the monitoring unit is able to be activated or deactivated by the functional unit, using a switching element. The switching element is able to be implemented by the setting or deleting of a bit. During an activated monitoring function, the functional unit is disconnected from the bus system by an access. For this, the monitoring unit activates an additional switching element, by which the connection of the functional unit to the bus system is interrupted. Here too, it has proven problematical that likewise separate switching elements have to be provided in the connection between the functional unit and the bus system, so that the functional unit is able to be decoupled from the bus system in the error case.
In addition, from the prior art, monitoring concepts for functional units are known, e.g., for motor vehicle control units, in which the monitoring unit triggers a reset in the error case. As a result of the reset, the functional unit runs up and thereafter attains its operational state. If the error of the functional unit continues to exist, the monitoring unit detects the error only in the newly operational state, and only then does it trigger again a reset of the functional unit. The forwarding of data by the functional unit via the bus system is only prevented for a short period of time during the reset state, since only in this state are the input/output connection positions (so-called ports) of the functional unit inactive. Thus, in the known method, a faulty functional unit may possibly forward faulty data via the bus system, even though the monitoring unit has detected an error of the functional unit. This may lead to safety-relevant situations in the control of the operational sequences.
An object of the present invention is to provide preventing of the forwarding of data by the functional unit via the bus system safely, reliably and in a simple manner.